p#back-to-top{
  position:fixed;
  bottom:50px;
  right:50px;
}
p#back-to-top a{
  text-align:center;
  text-decoration:none;
  /*color:#d1d1d1;*/
  display:block;
  /*width:300px;*/
  /*使用CSS3中的transition属性给跳转链接中的文字添加渐变效果*/
  -moz-transition:color1s;
  -webkit-transition:color1s;
  -o-transition:color1s;
}
/*p#back-to-top a:hover{
  color:#979797;
}*/
p#back-to-top a span{
  background: url(../images/arrow_up.png) no-repeat center center;
  border-radius:30px;
  display:block;
  height:60px;
  width:60px;
  margin-bottom:5px;
  /*使用CSS3中的transition属性给<span>标签背景颜色添加渐变效果*/
  /*-moz-transition:background1s;*/
  /*-webkit-transition:background1s;*/
  /*-o-transition:background1s;*/
}
#back-to-top a:hover span{
  background:url(../images/arrow_up.png) no-repeat center center;
}